Following speeding up and growing in size, a disc brake is frequently used as a braking device for a land transportation vehicle such as a railway vehicle, an automobile or a motorcycle. The disc brake is a device that produces a braking force by friction derived from the sliding contact between a brake disc (hereinafter, also simply “disc”) and a brake lining (hereinafter, also simply “lining”). In a case of the disc brake for the railway vehicle, the braking force is generated by pressing the lining, by a brake caliper (hereinafter, also simply “caliper”), against a frictional surface of the disc which has been mounted and fixed to a wheel or an axle. In this manner, the rotation of the wheel or the axle is slowed or stopped so that the speed of the vehicle is controlled.
Normally, the friction member of the lining is gradually worn away as a result of repetition of braking. However, if the friction member is partially worn away, braking performance becomes unstable. Therefore, to prevent the partial wear of the friction member, it is preferable that a pressing load is uniformly applied to the entire regions of the friction member during braking.
Furthermore, during braking, temperatures of the frictional surfaces of the lining and the disc increase by frictional heat. This temperature increase tends to be more conspicuous in conditions in which a braking load increases, to be specific, in conditions in which the traveling speed of the vehicle is high or in which the vehicle weight is heavy. In the actual traveling, it is desired to prevent thermal damages on the lining and the disc and to improve the durability of the lining and the disc. To this end, it is necessary to make the contact between the lining and the disc as uniform as possible and to reduce the frictional heat generated as a result of the contact during braking.
The caliper includes caliper arms extending to stride over the disc and the caliper arms hold linings, respectively. The calipers are mainly classified into a floating type and an opposed type, depending on the arrangement configuration of a drive source, for example, pistons or diaphragms, for pressing the lining against the disc. In a case of the floating type, the pressing drive source such as the pistons or diaphragms is provided only on one of the caliper arms each holding the lining. In a case of the opposed type, the pressing drive sources such as pistons or diaphragms are provided on both caliper arms, respectively.
For the railway vehicle, the disc brake using the floating caliper is often used. The disc brake will be described while referring only to the disc brake of the floating type.
FIG. 1 shows an example of a configuration of a conventional disc brake for a railway vehicle, illustrating one side thereof on which the pressing drive source is not provided. In the figure, FIG. 1(a) is a plan view in which a lining is viewed from a front surface side, FIG. 1(b) is a plan view in which the lining is viewed from a back surface side, FIG. 1(c) is an enlarged cross-sectional view taken along A-A of FIG. 1(a), and FIG. 1(d) is a cross-sectional view in a state in which the lining shown in FIG. 1(c) is detached from a caliper arm.
A conventional lining (hereinafter, “conventional type lining”) 12 shown in FIG. 1 is configured to include a friction member 3 that faces a frictional surface 1a of a disc 1, a base plate 14 having a fixed thickness and holding the friction member 3 on a front surface 14a, and a guide plate 15 fixedly provided at the center of a back surface 14b of the base plate 14. In FIG. 1, it is shown that a plurality of small-block-shaped friction members 3 are arranged, i.e., pairs of friction members 3 are arranged in a radial direction of the disc 1 and seven friction members 3 are arranged in a circumferential direction of the disc 1, that is, 14 friction members 3 are arranged in all. The friction members 3 are attached to the base plate 14 by rivets 6, respectively. A spring member may be arranged between the friction members 3 and the base plate 14.
The conventional type lining 12 is mounted to a lining holder (hereinafter, also simply “holder”) incorporated into each caliper arm, and set in a state in which a frictional surface 3a of each friction member 3 faces the frictional surface 1a of the disc 1 in parallel. As shown in FIGS. 1(c) and 1(d), on the side on which the pressing drive source such as pistons is not provided (hereinafter, also “non-pressing-drive-source side”), a holder 8 is integrally incorporated into the caliper arm 7, and a concave portion 8b that accommodates therein the guide plate 15 of the lining 12 is formed in this holder 8. The guide plate 15 of the lining 12 is set in a state in which upper and lower edges 15b and 15c of the guide plate 15 are engaged with upper and lower edges 8d and 8e of the concave portion 8b of the holder 8, respectively while a back surface (a surface that is on a back surface side relative to the lining) 15a closely contacts a bottom surface (a surface that is on a front surface side relative to the lining) 8c of the concave portion 8b of the holder 8. Such strong coupling of the guide plate 15 with the concave portion 8b of the holder 8 enables the non-pressing-drive-source side lining 12 to be strongly held to the holder 8 directly incorporated into the caliper arm 7.
Meanwhile, on the side on which the pressing drive source is provided (hereinafter, also “pressing-drive-source side”), a holder is attached to the pressing drive source, and a concave portion similar to that on the non-pressing-drive-source side is formed in this holder. Similarly to the non-pressing-drive-source side, the strong coupling of the guide plate with the concave portion of the holder enables the pressing-drive-source side lining 12 to be strongly held to the holder incorporated into the caliper arm via the pressing drive source.
In the conventional disc brake configured as described above, during braking, on the pressing-drive-source side, the pressing drive source is actuated, whereby a pressing force is loaded onto the lining 12 from the pressing drive source and the lining 12 is pressed against the disc. On the other hand, as shown in FIG. 1(c), on the non-pressing-drive-source side, a reaction force to the pressing force on the pressing-drive-source side is applied to the caliper arm 7, and the caliper arm 7 slidably moves toward the disc 1 (see a white arrow in FIG. 1(c)) and the lining 12 is pressed against the disc 1. At this time, on both the pressing-drive-source side and the non-pressing-drive-source side, the pressing force loaded onto the lining 12 directly acts on the guide plate 15 of the lining 12 via the holder 8 of the caliper arm 7. That is, the pressing force loaded onto the lining 12 does not directly act on the base plate 14 of the lining 12 but intensively acts on the guide plate 15 of the lining 12 because of a structure of a mounted portion of the lining 12 to the caliper arm 7.
In the case of the disc brake using the floating caliper, on the non-pressing-drive-source side, a phenomenon occurs that the caliper arm 7 is bent to open as the lining 12 is pressed against the disc 1 during braking. Owing to this, the friction member 3 on the non-pressing-drive-source side exhibits a tendency that a higher load acts on a region corresponding to an outer circumferential side of the disc 1 (hereinafter, also “outer circumferential-side region”) than on a region corresponding to an inner circumferential side of the disc 1 (hereinafter, also “inner circumferential-side region”). This particularly accelerates the wear of the outer circumferential-side region of the friction member 3 and the partial wear of the friction member 3, and even probably accelerates the partial wear of the disc 1.
To tackle these problems, various types of disc brakes with improved structures have been proposed recently with views of making uniform the pressure of the contact surfaces between the lining and the disc during braking.
For example, each of Patent Literatures 1 and 2 discloses a disc brake configured as follows. In anticipation that the caliper arm is bent to open on the side on which pistons serving as the pressing drive force are not provided during braking, the friction member is mounted to the holder of the caliper arm in a state in which the frictional surface of the friction member is inclined at a predetermined angle with respect to the frictional surface of the disc. In a case of Patent Literature 1, by changing the shape of the holder without changing the structure of the lining, the frictional surface of the friction member is inclined with respect to the frictional surface of the disc. In a case of Patent Literature 2, by changing the thickness of the friction member of the lining without changing the structure of the holder, the frictional surface of the friction member is inclined with respect to the frictional surface of the disc. According to such a disc brake, during braking, the contacts of the friction member with the disc starts from the inner circumferential-side region, and the frictional surface of the friction member contacts the frictional surface of the disc substantially in a parallel state by the bending of the caliper arm to follow the applied load. As a result, the surface pressure is made constant over the entire regions of the friction member.
However, in the disc brakes described in Patent Literatures 1 and 2, at the beginning of braking, the inner circumferential-side region of the friction member contacts the disc but the outer circumferential-side region thereof does not contact the disc. Owing to this, the partial wear of the friction member still probably occurs.